The invention relates to the dewatering of naturally moist crude peat. Particularly, it relates to a method which can reduce the water content of crude peat to a level at which the peat is relatively easily combustible, in a single continuous process.
Dewatered peat may be used, for example, for heating purposes. For this application, a naturally moist crude peat from a peat bog with a water content of the order of 90% and over must be dewatered, and to be combustible without auxiliary heating, normally to a level of 45% to 55% water by weight depending on its quality; i.e., depending on the respective calorific value of its dry substance.
In one original method, peat was dewatered by piling the peat into mounds, and then into a so-called stacks which are left to dry in the open air, for an unforseeable length of time. Such a method was totally dependent upon the weather, and the amount of drying time required could not be foreseen. In a more modern method, the peat is given a preliminary dewatering mechanically by means of a press to a residual moisture content of 60% to 70% by weight and is then dried in the air if necessary. This method, also, is largely dependent on the weather and, like the previously mentioned method, takes up large storage areas and unforeseeably long drying times.
For industrial heating, whenever peat must be continually available as a fuel in large quantities, a proportion of another fuel with an higher calorific value can be added to a mechanically dewatered peat to form a self-combustible mixture, or a peat which has been given a preliminary dewatering is loaded onto a heating layer of a fuel of higher calorific value for combustion. As such fuels, coal, oil or gas can be used.
Peat which has been given a preliminary dewatering can also be dried thermally, for example in a fluidized bed drier, into a self-combustible product. The self-combustible peat obtained in this way is normally subsequently burned in a furnace, and a portion of the heat thus obtained may be drawn back off to heat the drier. In this process, approximately 50% of the available calorific value of the peat is lost on evaporation of the water in the drier.
The methods mentioned above are not very economical, because on evaporation of the high proportion of water of the peat which is to be burned in this way, a large proportion of its calorific value is lost, usually at least 800 Kcal for 1 liter of water evaporated.
A peat having a residual moistness of 45%-55% water can also be produced through so-called blending, in which a more moist peat, containing for example 60%-70% water--, is mixed with a drier peat; e.g., containing about 20% water obtained from other sources of supply. A desired average moistness of, for example, 45%-55% can be obtained in this way.
A further disadvantage of known dewatering techniques is that the dewatered peat is a loose, light, spongy bulk material, the transportation and storage of which not only take up large volumes, but is also extremely difficult. Further, it is expensive and dangerous because of the fire risk and the possibility of explosion. In addition, the peat continues to dry naturally; the fibres become brittle and fragile; and breaking of the fibres results in a powdery peat of poorer quality because of the damaged structure if it is used, for example, to improve cultivated ground. For these purposes, fibrous peat is required which, so far as possible, maintains its original, natural structure.
It is intended to use peat in large quantities for the reconstitution of areas which have been transformed into steppe or arid areas; e.g., on various such technical agricultural programmes in developing countries. An obstacle to all this is the hitherto unsolved question of economical and safe transportation of large quantities of peat over large distances.
It is indeed known to pack the peat--by whatever way it has been dewatered--in bales in plastic bags for transportation, which facilitates handling and restricts further drying out. This method is however costly, such that it is only justifiable today in the field of the relatively small requirement for horticulture. In terms of volume, it only entails small advantages in transportation, so that transportation over long distances, even by sea, would be very or too expensive.